Acute kidney injury (AKI) refers to a sudden, unexpected decrease in kidney function, and dialysis-requiring AKI is associated with a high risk of short-term death. Its clinical and public health importance is underscored by recent studies showing a rising incidence over time. Previous studies AKI have primarily focused only on outcomes during the AKI hospitalization, with little known about long-term outcomes, including risk of development and acceleration of chronic kidney disease, death and recurrent AKI. In response to RFA-DK- 07-009 "Ancillary Studies in the Natural History of Acute Kidney Injury," we propose to establish a Clinical Center as part of the Acute Kidney Injury Natural History Consortium. We will contribute 200 case subjects who suffered AKI and 200 matched controls. Our application is an ancillary study to ongoing NIDDK-sponsored clinical studies of AKI at Kaiser Permanente of Northern California and UCSF (R01 DK67126). Our four Specific Aims are: Aim 1: To sequentially determine the trajectory of kidney function for up to 4 years among patients who suffer acute kidney injury compared with appropriately matched controls. Aim 2: To assess the risks of death, cardiovascular events and other outcomes for up to 4 years between patients who suffer acute kidney injury compared with appropriately matched controls. Aim 3: To identify and/or validate biomarkers or other risk assessment tools for patients who will develop or have worsening chronic kidney disease, or other significant long-term morbidity or mortality after an episode of acute kidney injury. Aim 4: To contribute to a new central repository to preserve the data and biological samples to share with the scientific community for future analyses and/or biomarker studies in acute kidney injury. The particular strengths of this proposal include a very experienced research team with expertise in acute and chronic kidney disease epidemiology, a strong history of successful participant recruitment and retention into long-term follow-up studies, and a unique infrastructure at Kaiser Permanente of Northern California which provide critical information about kidney function trajectory before an episode of acute kidney injury.